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1. The capacity of a material or construction to withstand fire or give protection from it; characterized by its ability to confine a fire and/or to continue to perform a structural function.
2. (Brit.) The ability of a component of building construction to satisfy certain criteria, specified by the BSI, for a stated period of time.
3. According to OSHA: so resistant to fire that, for a specified time and under conditions of a standard heat intensity, it will not fail structurally and will not permit the side away from the fire to become hotter than a specified temperature.